cdnjs is one of the most widely used free public CDNs on the web. It is a community-run, open-source library-delivery service hosted on Cloudflare's network, and it lets a developer drop a single <script> tag into a page to pull in jQuery, Font Awesome, Lodash, or almost any popular open-source package without hosting a file. That convenience is exactly why “loads assets from cdnjs” is a useful detection signal: it tells you something concrete about how a team builds and ships its front end.
This guide walks through detecting cdnjs on a website—what it actually is, where it shows up in a page's source, how to spot it manually, and how a single DetectZeStack API call returns cdnjs along with the specific libraries and versions it is delivering. We will start with a one-line check you can run right now.
What Is cdnjs and Why Detect It
cdnjs (short for “CDN for JavaScript”) is a free, open-source content delivery service that mirrors thousands of popular front-end libraries and serves them from the cdnjs.cloudflare.com hostname. Where an infrastructure CDN like Cloudflare or Amazon CloudFront proxies a whole site's traffic, cdnjs does something narrower: it hands out versioned copies of other people's open-source code so a page does not have to bundle and self-host them.
